Tau Geminorum
Scientific overview
Tau Geminorum is a red giant in the constellation Gemini (Geminorum), lying about 321.02 light-years from Earth.
Class K. Cooler orange stars. Long-lived and abundant; many are stable hosts for planets. Such stars have surface temperatures around 3,700–5,200 K and appear orange to the eye.
Physical properties
| Spectral type | K2III |
| Luminosity class | III |
| Apparent magnitude | 4.41 |
| Absolute magnitude | -0.56 |
| Luminosity (Sun = 1) | 145 |
| Colour index (B−V) | 1.261 |
| Distance | 321.02 ly (98.43 pc) |
Values are real catalogue data; fields without a reliable value are omitted, never estimated.
Precision measurements
Astrometry and astrophysics from SIMBAD and Gaia DR3 · Gaia DR3 886479673643853952 · elevated RUWE
| Parallax | 8.3261 ± 0.1591 mas | SIMBAD · measured |
| Distance | 120.5 pc | Gaia · estimated |
| Proper motion (RA) | -30.725 mas/yr | SIMBAD · measured |
| Proper motion (Dec) | -48.515 mas/yr | SIMBAD · measured |
| Radial velocity | 21.27 ± 0.28 km/s | SIMBAD · measured |
| Spectral type | K2III | SIMBAD · catalogued |
| Effective temperature | 4687.6 K | Gaia · modeled |
| Radius | 26.8125 R_sun | Gaia · modeled |
| Surface gravity (log g) | 2.1565 log(cm/s^2) | Gaia · modeled |
| Metallicity [M/H] | 0.201 dex | Gaia · modeled |
| Right ascension (ICRS) | 107.8 deg | SIMBAD · measured |
| Declination (ICRS) | 30.2452 deg | SIMBAD · measured |
Full field-level provenance
- Parallax: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · plx_value · 2020yCat.1350....0G · direct catalogue measurement · retrieved 2026-07-11
- Distance: ESA Gaia astrometric survey · Gaia EDR3 · Bailer-Jones (2021) · external.gaiaedr3_distance · r_med_geo · row 886479673643853952 · Bayesian estimate · retrieved 2026-07-11
- Proper motion (RA): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · pmra · 2020yCat.1350....0G · direct catalogue measurement · retrieved 2026-07-11
- Proper motion (Dec): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · pmdec · 2020yCat.1350....0G · direct catalogue measurement · retrieved 2026-07-11
- Radial velocity: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · rvz_radvel · 2018yCat.1345....0G · direct catalogue measurement · retrieved 2026-07-11
- Spectral type: Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · sp_type · 1989ApJS...71..245K · catalogue identifier/value · retrieved 2026-07-11
- Effective temperature: ESA Gaia astrometric survey · Gaia DR3 · gaiadr3.astrophysical_parameters · teff_gspphot · row 886479673643853952 · model output · retrieved 2026-07-11
- Radius: ESA Gaia astrometric survey · Gaia DR3 · gaiadr3.astrophysical_parameters · radius_gspphot · row 886479673643853952 · model output · retrieved 2026-07-11
- Surface gravity (log g): ESA Gaia astrometric survey · Gaia DR3 · gaiadr3.astrophysical_parameters · logg_gspphot · row 886479673643853952 · model output · retrieved 2026-07-11
- Metallicity [M/H]: ESA Gaia astrometric survey · Gaia DR3 · gaiadr3.astrophysical_parameters · mh_gspphot · row 886479673643853952 · model output · retrieved 2026-07-11
- Right ascension (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · ra · 2020yCat.1350....0G · direct catalogue measurement · retrieved 2026-07-11
- Declination (ICRS): Centre de données astronomiques de Strasbourg (CDS) · SIMBAD · basic · dec · 2020yCat.1350....0G · direct catalogue measurement · retrieved 2026-07-11
measured = direct catalogue value · estimated = Bayesian inference (Bailer-Jones distance) · modeled = model output (Gaia GSP-Phot). Fields a source did not provide are omitted, never invented.
Evolution
A red giant is an evolved star that has exhausted core hydrogen and expanded enormously, cooling at its surface as it fuses heavier elements in shells.
Location in the sky
Knowledge connections
- In constellationGemini
- Orbited bytau Gem b
Related stars in Gemini
Sources
The primary and reference sources this topic draws on.
- HYG DatabaseHYG Database (Hipparcos + Yale Bright Star + Gliese), by D. Nash / astronexus
Aggregated, openly-licensed star catalogue combining Hipparcos, the Yale Bright Star Catalogue, and the Gliese Catalogue of Nearby Stars.
- HipparcosESA Hipparcos space astrometry mission
High-precision parallax, magnitude, and position for ~118,000 stars.